1. Field of the Invention
The field of the invention relates to a method of controlling astigmatism during eye surgery.
2. Brief description of the prior art.
Astigmatism is a condition of the eye caused by the nonspherical shape of the cornea. This causes it to refract light in different meridians at different distances. While all people have some degree of astigmatism, correction of the condition is sometimes required by eyeglasses, contact lenses or surgery. Most astigmatism is below three diopters. Surgical techniques for correcting astigmatism include, among others, refractive keratoplasty and radial keratometry.
Certain types of eye surgery unrelated to the correction of astigmatism require that incisions be made in the tissue adjacent the cornea or in the corneal tissue itself. Such incisions are often between twelve and fourteen millimeters in length, and generally follow the periphery of the cornea. Other types of surgery, such as phacoemulsification, require a three to four millimeter incision. Upon completion of the surgery, the incision is closed by a plurality of stitches which are typically spaced about two millimeters apart. Each stitch is oriented either substantially normal to the peripheral edge of the cornea or at an angle with respect thereto.
If a corneal wound closure is too loose following surgery, it will tend to leak fluids and thereby delay the patient's recovery. In site complications and post-operative astigmatism may also result. Tight closure will cause postoperative astigmatism due to the direction(s) of orientation of the stitches and the force the stitches impart upon the cornea.
A system of controlling astigmatism following cataract surgery is described in U.S. Pat. No. 4,127,109. The incision in the scleral area is often generally arcuate, which is typical of most relatively large incisions in this type of operation. The incision is closed by a length of suture material which provides an opposing continuous pattern. This pattern is said to produce a standard or no deviation of astigmatism from the pre-operative level.
The patented system requires the use of a length of suture material which includes a plurality of sets of closely spaced, parallel lines. By observing the suture through a microscope having a reticule disposed therein, the strain in the length of suture material can be determined. Strain and tension data must then be correlated to astigmatism changes.
Other methods of controlling corneal curvature are described in U.S. Pat. Nos. 4,671,276, 4,739,761 and 4,766,895. The '761 patent discloses the use of a cornea marker as part of a procedure for conducting radial and chordal refractive keratomy.